Why should you care? It makes it easier to determine whether your stats are up/down because of an industry-wide trend of if it’s something unique to you.

For example, suppose your traffic yesterday was much lower than normal. You could open analytics and then see that all of the traffic in your industry was lower. From there, you could figure out why (holiday, etc) and not stress out about it so much.

This feature will require you to opt-in — it won’t be enabled automatically (which is a good thing, privacy-wise). I’m still not seeing this option available in my Analytics, so please post in the comments when you see it in yours.